1. Technical Field of the Invention
The present invention relates to a bellows and a vacuum switch and, more particularly, to a bellows used for sealing a lever portion provided so as to pass through a wall of an apparatus or device.
2. Description of Prior Art
In general, as one means for transmitting driving force without losing air-tightness between two different spaces such as between vacuum and atmosphere, bellows are used in many cases. For example, in a vacuum switch, an operating mechanism extending out of the vacuum switch and a lever passing through the vessel, move a movable rod against a fixed rod in an up and down direction to contact or separate electrodes provided on the respective rods. In this case, a bellows is used around the movable rode for sealing between the outside and the inside of the vacuum switch.
Further, as a prior art concerning this technique, JP A 55-143727 is cited, for example.
In such a mechanism, in a case where a bellows is expanded and shrunken only in an axial direction thereof as shown in FIG. 1 of JP A 55-143727, any problem does not occur. However, in a case where the lever swings around a fulcrum of a main shaft to contact and separate a movable electrode and a fixed electrode as in the vacuum switch disclosed in other figures of the above-mentioned JP A 5-143727, that is, in a case where expansion and shrinkage of the bellows deform the bellows in a curved shape, the bellows is repeatedly deformed in the curved shape, so that stresses are concentrated in the vicinity of connecting portions of the bellows, that is, in the vicinity of the fixed portion at the lever side and a fixed portion at the vessel wall side, and there may occur a crack at those portions during operation for many years and the sealing between the both spaces may be destroyed.
In this case, it is a matter of course that the stress concentration will be damped by making the diameter of the bellows larger to some extent. To make the size of the bellows larger, however, is to make larger the apparatus or device using the bellows, which is disadvantageous.